CNN, 6/26/2012

Dealing with deep drug war wounds is a top issue on Mexico's presidential campaign trail, but the election results could have an impact on both sides of the Mexico-U.S. border.

As candidates across party lines suggest new strategies, like reducing violence and taking troops off the streets, some U.S. lawmakers say they're nervous that cross-border cooperation could wane after Mexican voters pick a new president July 1.

Last week, a Republican congressman told the head of the U.S. Drug Enforcement Administration that he was concerned about Mexico's "impending change in power."

And Sen. John McCain, R-Arizona, said in February that he feared at least one Mexican presidential candidate was not committed to continuing his country's campaign against organized crime.

Worries in Washington as Mexico's election looms are a reminder of the close ties binding the neighboring nations. The two countries share billions of dollars in trade and a border that stretches for nearly 2,000 miles. Millions of U.S. citizens travel to Mexico every year, and millions of Mexican immigrants -- legal and illegal -- live in the United States.

"Almost no other country affects the United States as much on a day to day basis as Mexico," said Shannon O'Neil, a Latin American studies fellow at the Council on Foreign Relations.

"What happens in Mexico is hugely important for the United States."

For nearly six years, a brutal drug war in Mexico with a staggering death toll of more than 47,500 people has dominated discussions between the two countries.